Implantable prosthesis

Abstract

The shaft surface of a cementlessly implantable prosthesis is provided with a large number of holes which are formed as blind or pocket holes. Each hole is surrounded by a bulb in the form of a crater edge. The bony tissue that grows into the holes and around the bulbs ensures a firm seating of the prosthesis over a long time. The holes are preferably oriented in such a way that the bone pegs that extend into them can take up a desired load which may be either a compressive or a tensile force. A tensile force exerted on the bone will stimulate its growth.

What is claimed is: 
     
       1. An implantable prosthesis, comprising: a shaft having a bone engaging surface;   a plurality of fine pocket holes, each of said holes having a top, a bottom, and a varying cross-sectional diameter, said holes being located in the bone engaging surface, said holes being closed at the bottom and open at the top, certain of said holes being generally bowl-shaped and generally circular in cross section from the bottom to the top of the hole, the cross-sectional diameter of the hole being smallest at the bottom of the hole and increasing toward the top of the hole, the hole at its top being surrounded by a relatively smooth and continuous crater-shaped bulb extending outwardly from said bone engaging surface, each bulb being larger in diameter than any other diameter of the hole.   
     
     
       2. The prosthesis of claim 1, wherein the holes have a diameter of about 25 to about 100 μm, and a depth of about 50 to 200 μm. 
     
     
       3. The prosthesis of claim 2, wherein the holes have a diameter of about 30 to about 60 μm, and a depth of about 50 to about 90 μm. 
     
     
       4. The prosthesis of claim 1, wherein the number of holes per mm 2  of the shaft surface is about 20 to about 100. 
     
     
       5. The prosthesis of claim 4, wherein the number of holes per mm 2  of the shaft surface is about 30 to about 50. 
     
     
       6. The prosthesis of claim 1, wherein under normal conditions a force is exerted by the prosthesis on a bone in a direction generally parallel to said surface of said shaft, and wherein at least a portion of said holes are oriented so that axes of the holes pointing to bases of the holes form acute angles with said direction of said force exerted by said prosthesis on said bone. 
     
     
       7. The prosthesis of claim 1, wherein the shaft surface is shaped as a rounded thread. 
     
     
       8. The prosthesis of claim 1, wherein the shaft is tapered with a shaft cross-section generally decreasing from a head to an end of the shaft. 
     
     
       9. The prosthesis of claim 1, wherein the shaft is made of a titanium alloy.